This invention relates to communication and control systems, and, more particularly, to a system for transmitting and receiving audio signals containing speech information over a pair of parallel channels with improved accuracy.
In various applications of the transmission of information, redundant transmission channels are available, and the quality of the transmission can be improved by sensing the presence of noise on one channel and thereupon switching the transmission to the other channel to increase signal-to-noise ratio. Of course, this technique is limited by the ability to sense the noise and distinguish it from the signals being transmitted.
Speech recognition equipments have recently begun to gain commercial acceptance in voice command applications. A speech recognition equipment is typically programmed to understand a restricted vocabulary of spoken words and to distinguish between these spoken words with a relatively high degree of accuracy. When a particular word from among the restricted vocabulary is spoken, the speech recognition equipment generates an occurrence indication which is indicative of the word which was spoken, and the occurrence indication is used to control a companion system. For example, the companion system may respond to the speech command by routing an object to a particular location which was spoken by an operator or by recording inventory information spoken by the operator.
A single speech recognition equipment can be timeshared from a number of operator stations so that operators at different locations can send oral commands over transmission channels to the speech recognition equipment. The speech recognition equipment responds, such as by feeding appropriate inventory or routing information (corresponding to the oral commands) to a computer or companion system. In this type of application two or more redundant channels may be available from each operating location, and it would be desirable to have the ability to detect the presence of noise on one channel so that an alternate channel could be selected for use in the transmission. For example, each remote location may transmit the speech information to the word recognition equipment over a radio link, with each link having two available frequency bands for the transmission. Typically, the frequencies available for use for this type of a setup are commercially allocated portions of the spectrum wherein power restrictions are in effect. At these allocated frequencies, cross-talk and interfering signals from unrelated two-way radio signals become a problem. Typically, the interfering signals would be of the form of speech, so conventional techniques wherein "noise" is detected in order to switch away from a "noisy" channel would not be viable since the very speech signals to be transmitted are characteristically similar to the expected noise. A problem, therefore, is how to make optimum use of redundant transmission channels where speech recognition equipment is employed at the receiver end.
It is an object of the present invention to provide a solution to this problem.